USDA Hardiness Zone 9b
Frost Dates for 85173 — Superior, Arizona
NOAA 1991–2020 normals from Superior, AZ (2,860 ft), 1 miles north.
Updated
A freeze (32°F) reaches Superior in 77% of winters. When it does, the first fall frost comes around December 28 and the last spring frost around January 18; after March 1 the chance of another is under 8%.
- Last spring frost
- January 18
- First fall frost
- December 28
- Winters with a freeze
- 77%
- Hardiness zone
- 9b
50%, in freezing years
50%, in freezing years
32°F or below, 1991–2020
25 to 30°F (-3.9 to -1.1°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 6%
- Snow per year
- 0.3"
median, 1991–2020
median, 1991–2020
1 of 16 observed
NOAA normal
Frost risk by date in Superior
In the 77% of winters that bring a 32°F night, half of springs at Superior, AZ see their last 32°F night by January 18; only one in ten is past it by December 19, and one in ten still has one after March 1. Counting the winters with no freeze at all, the risk of a 32°F night after March 1 is under 8% and after January 18 38%. The 42 days between the even-odds date and the one-in-ten date is the widest of the 98 Arizona stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.
In fall the first 32°F night comes by December 28 in half of years, as early as December 1 one year in ten, and holds off past February 1 one year in ten. A hard freeze of 28°F is less common: it came in 26% of winters. The freeze-free season lasts 342 days in a typical year, longer than at 90% of the 98 Arizona stations; it reaches 365 days one year in ten and falls short of 294 one year in ten. On average 3 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 31 days longer, to about February 18, and return around December 11. A 24°F night is unusual: 2% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F99% of yrs | Jan 8 | Jan 21 | Feb 1 | Feb 9 | Feb 18 | Feb 25 | Mar 4 | Mar 14 | Mar 31 |
| 32°F77% of yrs | Dec 19 | Dec 31 | Jan 4 | Jan 10 | Jan 18 | Jan 26 | Feb 3 | Feb 15 | Mar 1 |
| 28°F26% of yrs | too rare for a date | ||||||||
| 24°F2% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F99% of yrs | Nov 24 | Nov 29 | Dec 4 | Dec 8 | Dec 11 | Dec 15 | Dec 20 | Dec 25 | Jan 4 |
| 32°F77% of yrs | Dec 1 | Dec 10 | Dec 15 | Dec 22 | Dec 28 | Jan 1 | Jan 8 | Jan 19 | Feb 1 |
| 28°F26% of yrs | too rare for a date | ||||||||
| 24°F2% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Superior, AZ, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 85173 →Compare Superior with another place →
Weather by month in Superior
July is the warmest month at Superior, AZ, averaging 99°F by day and 77°F at night; December is the coldest at 62°F and 44°F. From March to November the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 19% of years.
Warmth for growing adds up to 7,546 growing degree days a year (base 50°F), more than at 69% of the 102 Arizona stations. 40% of them (2,994) have built up by the end of June, and July adds the most, 1,179. Precipitation totals 17.8 inches a year, most in August (2.6") and least in June (0.3"); May to September bring 38% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 62 | 44 | 2.2 | 48% | 1 | 140 |
| Feb | 65 | 46 | 2.2 | 19% | <1 | 178 |
| Mar | 72 | 49 | 1.9 | 6% | <1 | 336 |
| Apr | 78 | 55 | 0.5 | 2% | <1 | 500 |
| May | 87 | 64 | 0.5 | 0% | 0 | 786 |
| Jun | 97 | 73 | 0.3 | 0% | 0 | 1053 |
| Jul | 99 | 77 | 2.0 | 0% | 0 | 1179 |
| Aug | 97 | 77 | 2.6 | 0% | 0 | 1141 |
| Sep | 93 | 72 | 1.3 | 0% | 0 | 982 |
| Oct | 84 | 63 | 1.1 | 0% | 0 | 730 |
| Nov | 73 | 52 | 1.1 | 6% | <1 | 378 |
| Dec | 62 | 44 | 2.1 | 41% | 1 | 141 |
Monthly normals 1991–2020 at Superior, AZ (2,860 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Miami, AZ, 16 miles northeast of Superior and 700 feet higher, has a last frost 37 days later (February 24), a first frost 27 days earlier (December 1), a season 63 days shorter.
When it snows in Superior, Arizona
Measurable snow is rare here: only 1 of 16 winters from 1991 to 2020 recorded 0.1 inch or more at Superior, AZ, 1.4 miles away, so there is no typical first-snow date to plan around.
Where these figures come from
ZIP 85173 is 1 mile from Superior, AZ, which stands at 2,860 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 85173 in zone 9b, the band where the coldest night of the year averaged 25 to 30°F (-3.9 to -1.1°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.